Human immunodeficiency virus (HIV) is known for its impact on the immune system, leading to acquired immunodeficiency syndrome (AIDS). HIV can also affect the brain and nervous system, leading to neurological complications.
How HIV Harms Brain Cells
HIV primarily affects the brain by infecting immune cells residing within the central nervous system, rather than directly infecting neurons. Microglia and astrocytes, which are types of glial cells that support and protect neurons, are the main targets for HIV infection in the brain. These infected cells can then become a reservoir for the virus within the brain.
The virus enters the central nervous system early in the course of infection, often carried by infected immune cells like monocytes and T cells that cross the blood-brain barrier. This barrier normally restricts the passage of harmful substances into the brain, but HIV can compromise its integrity, allowing more infected cells to enter. Once inside, the infected microglia and astrocytes release inflammatory mediators, such as cytokines and chemokines, and neurotoxic substances. This leads to an inflammatory environment and oxidative stress, which can damage uninfected neurons and disrupt their function.
Neurological Changes and Symptoms
HIV infection can manifest neurologically in various ways, with HIV-Associated Neurocognitive Disorder (HAND) being a concern. HAND encompasses a spectrum of cognitive, motor, and behavioral changes. This spectrum ranges from asymptomatic neurocognitive impairment (ANI), where individuals show impaired performance on neuropsychological tests but maintain daily independence, to mild neurocognitive disorder (MND), which involves mild interference with everyday function. The most severe form is HIV-associated dementia (HAD), characterized by substantial impairment in daily activities.
Symptoms of HAND can include difficulties with attention, concentration, and memory. Individuals may experience slowed processing of information, problems with planning, and challenges in learning new skills. Motor symptoms can also occur, such as clumsiness, poor balance, and tremors. Behavioral changes, including apathy, lethargy, social withdrawal, irritability, depression, and anxiety, are also seen.
Beyond HAND, other neurological complications can arise. These include peripheral neuropathy, which involves damage to nerves outside the brain and spinal cord, leading to pain, numbness, or weakness in the limbs. Opportunistic infections, which take advantage of a weakened immune system, can also affect the brain, causing conditions like toxoplasmosis or cryptococcal meningitis.
The Role of Antiretroviral Therapy
Antiretroviral therapy (ART) has changed the impact of HIV on the brain. ART works by suppressing the viral load in the body, which also reduces the amount of virus in the central nervous system. This reduction helps to mitigate the inflammation and neurotoxicity that contribute to brain damage. Early initiation of ART is important, as it can help prevent or halt the progression of HIV-related brain damage.
While ART has made severe forms of HAND, such as HAD, less common, some individuals may still experience milder cognitive issues. This persistence of cognitive challenges, often referred to as “residual HAND,” can occur despite effective viral suppression. The continued presence of some viral activity or ongoing immune activation within the brain, even at low levels, may contribute to these milder symptoms. ART has transformed HIV into a manageable chronic condition, but ongoing research continues to explore ways to further improve neurological outcomes for people living with HIV.